Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3217
2017-01-23T06:23:32ZPT-axisymmetric photonic nanostructures
http://hdl.handle.net/2117/90240
PT-axisymmetric photonic nanostructures
Ahmed Waseem, Waqas Waseem; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis
Optical Parity-Time (PT-) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the P-symmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.
2016-09-27T13:50:04ZAhmed Waseem, Waqas WaseemBotey Cumella, MurielHerrero Simon, RamonStaliunas, KestutisOptical Parity-Time (PT-) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the P-symmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.Tunable wavelength-demultiplexer by tapered photonic crystal waveguide
http://hdl.handle.net/2117/85665
Tunable wavelength-demultiplexer by tapered photonic crystal waveguide
Hayran, Zeki; Turduev, Mirbek; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis; Kurt, H.
We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.
2016-04-14T11:57:27ZHayran, ZekiTurduev, MirbekBotey Cumella, MurielHerrero Simon, RamonStaliunas, KestutisKurt, H.We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
http://hdl.handle.net/2117/85442
Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
Jedynak, Maciej; Pons Rivero, Antonio Javier; García Ojalvo, Jordi
2016-04-08T14:43:13ZJedynak, MaciejPons Rivero, Antonio JavierGarcía Ojalvo, JordiUltrashort pulse chirp determination via transverse auto-correlation in SBN crystal
http://hdl.handle.net/2117/84721
Ultrashort pulse chirp determination via transverse auto-correlation in SBN crystal
Wang, Bingxia; Cojocaru, Crina; Inigo Sola, Inigo Sola; Wieslaw Krolikowski, Wieslaw Krolikowski; Yan Sheng, Yan Sheng; Vilaseca Alavedra, Ramon; Trull Silvestre, José Francisco
We determine the different initial chirp parameters of ultra-short pulses down to 30 fs via single-shot transverse auto-correlation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse auto-correlation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental results
2016-03-18T15:19:16ZWang, BingxiaCojocaru, CrinaInigo Sola, Inigo SolaWieslaw Krolikowski, Wieslaw KrolikowskiYan Sheng, Yan ShengVilaseca Alavedra, RamonTrull Silvestre, José FranciscoWe determine the different initial chirp parameters of ultra-short pulses down to 30 fs via single-shot transverse auto-correlation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse auto-correlation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental resultsAsymmetric light transmission by using 2D PT-symmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PT-symmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
2015-07-27T11:42:50ZTurduev, M.Botey Cumella, MurielHerrero Simon, RamonKurt, H.Staliunas, KestutisGiden, I.We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.Suppression of modulation instability by spatio-temporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatio-temporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
2015-05-29T15:05:10ZStaliunas, KestutisModulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.Beam focusing in chirped mirror with a defect
http://hdl.handle.net/2117/27767
Beam focusing in chirped mirror with a defect
Cheng, Yu Chieh; Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.
2015-05-06T09:53:50ZCheng, Yu ChiehStaliunas, KestutisRecently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.Excitation/inhibition patterns in a system of coupled cortical columns
http://hdl.handle.net/2117/27684
Excitation/inhibition patterns in a system of coupled cortical columns
Malagarriga Guasch, Daniel; Villa, Alessandro; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
We study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and all-to-all coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.
2015-04-30T08:53:32ZMalagarriga Guasch, DanielVilla, AlessandroGarcía Ojalvo, JordiPons Rivero, Antonio JavierWe study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and all-to-all coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.Beam focalization by chirped mirrors
http://hdl.handle.net/2117/27289
Beam focalization by chirped mirrors
Cheng, Yu Chieh; Peckus, Martynas; Kicas, Simonas; Trull Silvestre, José Francisco; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.
2015-04-13T14:59:48ZCheng, Yu ChiehPeckus, MartynasKicas, SimonasTrull Silvestre, José FranciscoCojocaru, CrinaVilaseca Alavedra, RamonDrazdys, RamutisStaliunas, KestutisA novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.Asymmetric transmission from a 2D PT-symmetric honeycomb nanostructure
http://hdl.handle.net/2117/24628
Asymmetric transmission from a 2D PT-symmetric honeycomb nanostructure
Botey Cumella, Muriel; Herrero Simon, Ramon; Turduev, M.; Zhao, D.; Giden, I.; Kurt, H.; Staliunas, Kestutis
We propose a simple realization of a 2-dimensonal (2D) PT-symmetric photonic structure: a honeycomb arrangement of alternating cylinders with gain or loss in a dielectric background. The structure provides a periodic modulation of the refractive index on the wave length scale, which combined with an anti-symmetric gain/loss distribution on the same scale, leads to non-reciprocal light coupling at resonance frequencies. Numerical simulations show asymmetric right-left transmission of light beams.
2014-11-10T10:26:15ZBotey Cumella, MurielHerrero Simon, RamonTurduev, M.Zhao, D.Giden, I.Kurt, H.Staliunas, KestutisWe propose a simple realization of a 2-dimensonal (2D) PT-symmetric photonic structure: a honeycomb arrangement of alternating cylinders with gain or loss in a dielectric background. The structure provides a periodic modulation of the refractive index on the wave length scale, which combined with an anti-symmetric gain/loss distribution on the same scale, leads to non-reciprocal light coupling at resonance frequencies. Numerical simulations show asymmetric right-left transmission of light beams.